The present invention relates to an optical disk exposure device, and more particularly, to a device for exposing a photoresist layer coated on a master disk of a stamper which is a mold for manufacturing optical disks, using optical fibers.
Various kinds of recording media are classified by the recording and reproducing methods used. In an optical recording and reproducing method using a laser beam, a laser beam is projected onto a signal surface comprised by pits arranged in a spiral on a surface of an optical disk, and reflected from the signal surface according to an optical signal, to thereby record and reproduce information. The optical disk is made of a transparent resin material such as polymethylmethacrylate or polycarbonate, and includes a transparent substrate having an information recording surface of pits of a predetermined pattern, a reflection film formed by coating a metal on the transparent substrate by deposition or sputtering, and a protection film formed on the reflection film.
The transparent substrate of the optical disk is manufactured by injection-molding, using a mold called a stamper having the same patterns as the pit patterns. The stamper includes a master disk having a photoresist layer of the same patterns as the pit patterns formed on the information recording layer of the transparent substrate thereon, and a nickel film coated to a predetermined thickness on the upper surface of the photoresist layer.
In manufacturing such a stamper, a conventional exposure device shown in FIG. 1 is used to form pits of a predetermined pattern on the photoresist layer.
Referring to FIG. 1, a laser beam projected from a laser beam source 23 is selectively passed or blocked by a shutter 24. Then, the laser beam passing the shutter 24 is reflected toward an object lens 21 by a dichroic filter 22, and the reflected beam is focused in the object lens 21 to reach a photoresist layer 12. In this manner, the photoresist layer 12 formed on the upper surface of the master disk 11 is exposed to the laser beam in a predetermined pattern.
During exposure of the photoresist layer 12, the laser beam is focused as follows. The laser beam generated in a focus correcting laser beam source 26 reaches the photoresist layer 12 of the master disk 11 through a half mirror 25, the dichroic filter 22, and the object lens 21. The beam reflected from the photoresist layer 12 is projected back to a focus correcting optical means 27. When the beam is projected to the focus correcting optical means 27, an electrical signal is generated. An actuator (not shown) of the object lens 21 is driven by this electrical signal, thereby correcting the focus.
When the photoresist layer 12 of the master disk 11 is exposed to the laser beam as described above, a nickel plated film is formed on the upper surface of the photoresist layer 12, thereby obtaining a stamper.
However, a problem with the conventional exposure device is that the device is expensive and complicated due to the need for a precise optical system for correcting the focus of a laser beam. Another problem is that since the laser beam is focused by the object lens thereby limiting the degree to which the size of the spot of the beam can be decreased, the recording density of the master disk cannot be increased.